1. Field of the Invention
The present invention relates to a display, and more particularly to a light source driving circuit of light emitting semiconductor and a backlight module.
2. Description of Related Art
LCD display panel cannot generate light itself, it requires utilize the backlight method to project the light to the display panel and makes the display panel produce a brightness, and the brightness should distribute evenly to the display screen to obtain a good picture. Currently, the backlight source of the LCD display panel is mainly divided into two kinds of LED and CCFL. Comparing to the CCFL backlight, the LED backlight source has low power consumption, long life, thin, and good optical properties. Therefore, utilizing white LED as the backlight source of the LCD display is becoming the direction of development of LCD TV.
As shown in FIG. 1, in the LED backlight driving circuit, a current amplitude of the LED is decided by a reference voltage Va required by the constant current driver IC and the current limiting resistor R0, i.e., 1=Va/R0. The reference voltage Va is provided by an external circuit to the constant current driver IC. The current flowing through the LED determines the emitting brightness of the LED. However, the brightness of the LED backlight required in the 2D display mode and the 3D display mode is not the same. Thus, under the current limiting resistor R0 is determined, the reference voltage Va required at the 2D display mode and the 3D display mode is not the same.
In the 2D display mode, The MOS tube Q12 is turned off, and MOS tube Q11 is turned on. At this time, resistors R11, R12 and R13 are in working condition. The R12 and R13 are in parallel and divide a voltage so that the voltage value Va is relatively small. In the 3D display mode, the MOS tube Q12 is turned on, and the MOS tube Q11 is turned off. At this time, only the resistors R11 and R12 are in working condition, so that the Va voltage value is relatively larger than the Va voltage value in the 2D display mode. In addition, a PWM dimming signal is for changing and adjusting the duty ratio of the LED current such that the current flowing through the LED becomes smaller in the average value in order to achieve the effect of reducing the backlight brightness.
The manner described above can achieve that obtaining different Va voltage values in the different display modes and the PWM dimming signal, and obtaining the LED brightness in the corresponding display mode. However, when switching between the 2D display mode and the 3D display mode, the switching speed is very fast. When switching the LED brightness in the 2D display mode to the 3D display mode, or switching, the LED brightness in the 3D display mode to the 2D display mode, the current flowing through LED change suddenly such that the brightness of the LED backlight will change suddenly, which could easily lead to a strong visual impact to the viewer, and reducing the viewing experience.